a) Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device that is applied to an IC, a power transistor, a thyristor, a diode, an oscillating element, a photodiode, a light emitting diode, a semiconductor laser, a thermistor, or a sensor. In particular, the present is suitable to a method for manufacturing a semiconductor device with high power consumption.
In addition, the present invention relates to a semiconductor lead frame suitable for direct use in implementing the semiconductor manufacturing method, and a method for manufacturing the semiconductor lead frame.
b) Description of the Related Art
In a conventional semiconductor lead frame, the ends of inner leads of a relatively thin lead section are located directly above the periphery of a thick flat rectangular chip pad section, with outer leads extending radially. A semiconductor chip is stuck to the chip pad section, and its thickness is increased to improve heat radiation.
FIG. 8 is a top view of a conventional lead frame, and FIG. 9 is a sectional view taken on line B--B in FIG. 8. A chip pad section 16 and a lead section 27 are conventionally manufactured as separate parts by means of press punching. The chip pad section 16 is a thick rectangular plate, and a semiconductor chip (not shown) is mounted on a top surface 161 at a semiconductor mounting position 162 by means of sticking. Cylindrical assembly pins 163, 164, 165, and 166 integrally stand from the four corners of the top surface 161 of the chip pad section 16.
Two lead sections 27 and 28 are manufactured as separate parts by means of press punching. Tie bars 273 and 283 are located between inner leads 271 and 281, the tips of which are located at the semiconductor mounting position 162 and outer leads 274 and 284 protruding out after packaging, in order to restrain the inter-lead positions from varying while preventing resin from protruding during resin packaging. In addition, the tips of the outer leads 274 and 284 are respectively coupled together by outer bars 275 and 285 to restrain the inter-lead positions from varying. Assembly pieces 81, 82, 83, and 84 are integrally formed at the lateral ends of the lead sections 27 and 28 and protrude toward the tips of the inner leads. Assembly holes 811, 821, 831, and 841 are drilled near the tips of the assembly pieces 81, 82, 83, and 84, respectively.
As shown in FIG. 9, after an assembly pin 166 of the chip pad section 16 has been inserted into the assembly hole 841 in the assembly piece 84 of the lead section 28, the tip of the assembly pin 166 is compressed and crushed to form a large-diameter portion 167, which is used to fix the assembly piece 84. If a top surface 842 of the assembly piece 84 is used as a curved surface for press punching while a bottom surface 843 is used for a burr surface for press punching, the neighborhood of the tips of the inner leads 281 is flattened and compressed to increase the area of the plane portion in order to reduce inappropriate wire-bonded connections. `A burr surface` means a surface side having a burr. If a sheet material with one surface Au- or Ag-plated is used, the lead frame is assembled in such a way that the plated layer lies in the top surface.
Furthermore, a conventional semiconductor device manufacturing method obtains a semiconductor device by sticking and fixing a semiconductor chip on the chip pad section of the conventional semiconductor lead frame, carrying out wire bonding to connect each electrode on the semiconductor chip to the end of each inner lead of the semiconductor lead frame using a gold wire, and then executing resin molding to seal the lead frame with a hot-melted resin except for the outer lead section.
Strict dimensional and locational accuracy, however, is required for the assembly pins formed on the chip pad section and the assembly holes formed in the lead section. These components are difficult to design, manufacture, and manage, and have a relatively low yield.
In addition, the assembly of the chip pad and lead sections is automated, but errors are likely to occur during the supply, alignment, and caulking of small parts.
As a result, a trade-off is required between the accuracy and yield of assembled lead frames, and it is difficult to meet both of them.